1. Field of the Invention
The present invention pertains to the field of integrated circuits. More particularly, this invention relates to cooling an integrated circuit on a printed circuit board (PCB) with little or no external power needed for cooling.
2. Background
Advances in integrated circuit technology have led to faster clock frequencies and greater densities of transistors. These increases result in a corresponding increase in heat generated by integrated circuits. With large amounts of heat being generated, cooling becomes a problem.
Advances in integrated circuit technology have also led to smaller, more portable computer platforms like notebook computers. Portability depends in part on power consumption. The longer a notebook computer can operate on its battery, the more portable the notebook computer is. Therefore, reducing the amount of power consumed for cooling is also important.
Typically, integrated circuits are cooled by either active or passive cooling devices. An active cooling device is defined as a cooling device that uses additional power in the system being cooled, where a passive cooling device does not use additional power. The ability of a passive device, such as a heat sink mounted onto an integrated circuit package body to dissipate heat, is constrained by its size. Thus a passive device for use in a notebook computer is constrained in its ability to dissipate heat. An active cooling device, such as a fan, can be used to dissipate larger amounts of heat by blowing air across the integrated circuit or heat sink. As the integrated circuit generates more heat and a larger heat sink is employed, greater air flow is required. Unfortunately, to increase air flow, more power is consumed.
Thermoelectric modules (TEM) have been used as active cooling devices. By placing a TEM between an integrated circuit and a heat sink and supplying the TEM with a current, the TEM transfers heat from the integrated circuit to the heat sink. The phenomenon is called the Peltier effect. The TEM consists of ceramic plates with p-type semiconductor material and n-type semiconductor material between the plates. The elements of semiconductor material are connected electrically in series. When a DC voltage is applied to the semiconductor material, electrons pass from the p-type material to the n-type material. The elements are arranged in a manner such that when a DC voltage is applied, heat is transferred from one side of the TEM to the other. The rate of transfer is proportional to the current and the number of p-n junctions. Unfortunately, active cooling using a TEM also consumes additional power.
Thus, a cooling solution for cooling an integrated circuit device, such as those employed in notebook computers that reduce the consumption of battery or line power, is needed.